This application relates to the art of switch assemblies and, more particularly, to thermostatic switch assemblies of the type having temperature responsive bimetals that actuate switches. The invention is particularly applicable to thermostatic switch assemblies wherein the bimetals are heated by a thermistor having a positive temperature coefficient. However, it will be appreciated that the invention has broader aspects and can be used with other types of heaters or no heater at all.
Three thermostatically operated switches are often required to provide sequential timing of resistance heating elements and fans in electric furnaces, air conditioners and heat pumps. Voltage applied to a heater circuit activates one or more bimetals to open or close switch contacts. Removal of the voltage allows the bimetal to cool for returning the switch contacts to their normal state.
Requirements for three thermostatically operated switches are commonly met by using one thermostatic switch assembly having two thermostatically operated switches, and another separate thermostatic switch assembly having one thermostatically operated switch. Each individual thermostatic switch assembly requires its own heater for the bimetal and two such heaters draw significant in-rush current. Two individual thermostatic switch assemblies also occupy a larger space envelope and require individual mounting.
It Would be desirable to eliminate the need for two individual thermostatic switch assemblies in applications requiring at least three thermostatically operated switches. It would also be desirable to eliminate the need for more than one bimetal heater in order to significantly reduce the in-rush current.